1. Field of the Invention
The present invention relates to a display device and a method for manufacturing the display device. In particular, the present invention relates to a display device utilizing organic electroluminescence (EL) (the device is referred to as organic EL display device) and a method for manufacturing the display device.
The present invention relates to an organic EL display device including a high-definition display panel and a method for manufacturing the organic EL display device. In particular, the present invention relates to an organic EL display device in which a shape of a partition separating pixels and a height of the partition are adjusted, and a method for manufacturing the organic EL display device.
2. Description of the Related Art
In recent years, color organic EL display panels using an oxide semiconductor for a TFT have been suggested. Varied development has been conducted. For example, in order to keep high color reproducibility or to achieve high-definition display by extracting light with high color purity, a display panel in which a white organic EL element, three color filters of red (R), green (G), and blue (B), and a microcavity structure utilizing multiple reflection are combined has been formed. When the color filter and the microcavity structure are combined, reflection of external light can be reduced, and light emitted from the white organic EL element can be extracted efficiently.
The microcavity structure is a technique in which the optical path length is optimized in accordance with the light wavelength of three colors of RGB (e.g., R: 700 nm, G: 550 nm, and B: 440 nm) to increase the intensity of light with a desired wavelength and extract the light. For example, optimization of the optical path length is conducted by changing the thickness of a transparent conductive layer. The thickness of a transparent conductive layer in a pixel where red light is emitted is larger than that in a pixel where green light is emitted.
Further, in a large-sized color organic EL display panel, a top emission method is suggested. A top emission method is a method in which light is extracted from a side opposite to a substrate where a TFT is formed and thus part of light emitted from the pixel is not blocked by a TFT, a wiring, and the like. Accordingly, a top emission method enables the aperture ratio to be improved as compared with a bottom emission method in which light is extracted from a substrate side where a TFT is formed. One of features of a top emission method is that a color filter can be used relatively simply.
A method in which a color filter is overlapped with a white organic EL element enables color separation of three colors of RGB relatively easily as compared with a separate coloring method in which high-definition coloring is separately performed with use of a metal mask to form light-emitting layers emitting three colors of RGB independently.
As an example of a structure of a white organic EL element, a tandem light-emitting element in which a plurality of light-emitting units and an intermediate unit are stacked between an anode and a cathode can be given. Each of the units is formed with a plurality of deposited layers. Light from the whole tandem light-emitting element can be white light by overlapping of emission colors emitted from the plurality of light-emitting units. For example, a white organic EL element can be formed with a stacked structure including a B unit formed with four deposited layers, an intermediate unit formed with four deposited layers over the B unit, and R and G units formed with eight deposited layers over the intermediate unit.
In Patent Document 1, a highly reliable display device in which shape defects of a pixel electrode are prevented to achieve high-definition display is disclosed. A partition having a thin portion and a thick portion is formed with a single layer. With the thin portion, poor coverage of a light-emitting layer at a boundary between the pixel electrode and the partition is suppressed. The thick portion of the partition supports a deposition mask to suppress twist or deflection of the deposition mask, which prevents damage such as a blemish caused by the deposition mask to be generated on a pixel electrode surface.